To harness the power of the wind. Quite useful if you don't have enough slaves to row you across the sea.
There is no evidence to say that the Egyptians made the first sail.
No one can say who, where or when the first sail was made. Consequently its shape is not know either.
usually dacron.
China
It was difficult to sail the Nile in Nubia because of the many cataracts,rocks,and waterfalls. This made navigation difficult to sail.
Sailing has been around since prehistoric times, therefore the name of the person who made the first sail boat is not recorded.
We had some sails made for the boat at the sail loft. Then we went aloft to set sail.
Nowadays mainly from GRP
He designed a sail that was more efficient. It could maneuver better and was able to maintain better speeds. It made his sail-loft the most successful sailing business in Philadelphia. This sail was not patented.
Wut made ships sail in the wind was that using a persicet sail or flag will pick up the wind and will push the air out and sail..just like u swinging on a swing 
No sailing ship can sail directly into the wind. However by rigging the sails correctly the vessel can be made to sail more closely to the wind.
It's supposed unlucky to sail on a Friday because it was just a myth made by the Greek.